The present invention relates to miniature current overload fuses which, whether they are rated to carry only a few amperes or as much as 30 amperes, occupy a space which is only a fraction of the space occupied by the conventional glass envelope cylindrical fuses.
An overload fuse capable of carrying currents of the above range of magnitudes commonly comprise a sealed cylindrical glass envelope with cylindrical terminals projecting from the ends thereof and a fuse link extending between the fuse terminals within the sealed cylindrical envelope. Fuses of this type having current ratings of 10--30 amperes commonly have lengths of the order of magnitude of over one inch and, together with the mounting terminals with which they are associated, an overall width of approximately one quarter inch and higher. Some of the disadvantages of this type of fuse are the large space requirements for mounting the same and difficulty in removing them from mounting clips.
A marked improvement in overload current fuses of the ratings referred to were made in the fuse designs disclosed in U.S. Pat. No. 3,909,767. In the fuses disclosed in this and other related patents, the terminals of the fuse project in spaced confronting relation from a narrow housing acting as a convenient insulated gripping means. The terminals plug into less expensive and less bulky socket clips than the connectors needed for conventional cylindrical type fuses.
This unique fuse is preferably a two-piece assembly comprising the housing and plug-in fuse metal element including a plate-like body of fuse metal having a pair of spaced confronting terminal blade portions, current carrying extensions at the inner end portions of the pair of terminal blade portions and a fuse link portion of reduced thickness interconnecting the current-carrying extensions. The housing has confronting closely spaced main side walls interconnected on three sides by narrow walls, the fourth side having a narrow opening preferably extending for substantially the full length thereof for insertion of the plug-in fuse element. The main walls of the housing are preferably staked into apertures formed in the plug-in fuse element. The terminal blade portions of the plug-in fuse element project from the open side of the housing and plug into socket clips in the mounting panel. When the fuse assembly is plugged into the mounting panel clips, the mounting panel forms a barrier, preventing blown fuse metal from spewing outside of the housing through the open side of this housing covered by the mounting panel. However, some users prefer that the housing completely enclose the plug-in fuse element so that the housing rather than the mounting panel prevents passage of blown fuse metal to the outside of the housing.
As disclosed in U.S. Pat. No. 3,909,767, the plug-in fuse element is formed from a fuse metal strip in which successive longitudinal portions of the strip are progressively die stamped to form initially interconnected plug-in fuse element blanks. The housing for the endmost blank is applied thereover before the blank is severed from the strip. The housing is staked or otherwise anchored to the blank, following which an almost completed fuse assembly is separated from the strip, to expose the next blank of the strip for insertion of a similar housing.
Various approaches have been suggested for completely enclosing the fuse link portion of a plug-in fuse element. For example, a housing could be a molded body of synthetic plastic material intimately surrounding the fuse link. However, this complicates the fabrication process and the intimate surrounding of the fuse link with synthetic plastic material could adversely affect the blowing characteristic thereof. Another approach is to form the housing in two parts, the main part having an open top and a pair of openings in the bottom thereof for receiving insertion of the terminals of the plug-in fuse element to be supported in the housing. A cover is then inserted over and ultrasonically welded to the top of the housing. This construction was found unsatisfactory for a number of reasons including the fact that sometimes the housing cover would come loose from the main housing part. Also, the assembly required for this construction is more complicated and expensive than desired. It is, accordingly, an object of the invention to provide a fuse assembly preferably of the type just described and disclosed in U.S. Pat. No. 3,909,767, and further wherein the housing forms a substantially complete enclosure for the fuse link portion of the plug-in fuse element so that blown fuse metal cannot gain access to the exterior of the fuse assembly housing. A related object of the invention is to provide a fuse assembly as just described that lends itself to the mass production thereof in a similar way to which the plug-in fuse assembly disclosed in U.S. Pat. No. 3,909,767 is fabricated.